Bump sprockets-rails from 3.2.2 to 3.4.2

[javierm]

References

• The sprockets-rails gems changed its way to process CSS files in Process css files so that they get digested paths for asset files rails/sprockets-rails#476 and added an option to keep the old behavior in Add assets.resolve_assets_in_css_urls configuration option to allow disabling AssetUrlProcessor rails/sprockets-rails#489
• The new way to process CSS files breaks CKEditor icons, as reported in Wrong asset path being requested galetahub/ckeditor#919
• The sprockets-rails gem will need to be added as an explicit dependency in Rails 7, as mentioned in the Upgrading Ruby on Rails guide

Objectives

• Avoid breaking CKEditor every time we (or Dependabot) run bundle update <gem> and accidentally update sprockets-rails
• Make sure we don't break CKEditor when upgrading to Rails 7.0

[javierm]

After merging this pull request, we're getting a warning when compressing assets on production:

WARN -- : Removed sourceMappingURL comment for missing asset
'graphiql/rails/push-pull-async-iterable-iterator.esm.mjs.map' from
gems/graphiql-rails-1.8.0/app/assets/javascripts/graphiql/rails/graphiql-1.4.2.js

There are at least two possible ways to remove this warning.

First, we could start using Terser instead of Uglifier to compress JavaScript. Not sure why, but at some point I thought using Terser removed the warning. Apparently, it doesn't.

Second, we could remove graphiql-rails from production, so it's only available in development. This is actually what's recommended in the graphiql-rails README. We enabled graphiql-rails on production in #1659.